The present invention generally relates to systems for delivering electrical power to equipment, such as computers and communications equipment, associated with a mobile site such as a vehicle.
Any of a variety of applications have arisen that are enhanced by placing support equipment, such as computers and communications equipment, in a vehicle to provide the operator of the vehicle with increased connectivity to remotely available information and/or personnel. For example, it has been found to be beneficial to provide police, fire and emergency vehicles with such equipment to rapidly establish routing, to remotely access desired data and to communicate with command or other support personnel. Similarly, it has been found to be beneficial to provide service and/or route vehicles with such equipment to establish routing, to provide desired services and to access remote data useful in performing such services, among others.
Irrespective of the application being implemented, it is conventional practice to couple such equipment with the electrical system of the vehicle that receives such equipment. The electrical system of the vehicle (i.e., the alternator or generator, the voltage regulator, the storage battery, etc.) can then be used to conveniently supply the direct current (DC power) which is needed to operate the equipment associated with the vehicle.
In practice, however, it has been found that while such systems work well to supply the power necessary for operating such equipment while the vehicle is in operation, difficulties can arise when operation of the vehicle is discontinued (i.e., the engine is shut off) but continued operation of the associated equipment is desired.
For example, electrical equipment which remains in operation after the vehicle has been shut off will continue to draw power from the electrical system of the vehicle. Because the vehicle is no longer running, the vehicle's electrical system will no longer be charging. Over an extended period of time, this can reduce the voltage produced by the storage battery associated with the vehicle's electrical system to a level which is no longer sufficient to re-start the vehicle. Because this is generally considered to be an undesirable result, at times presenting an unacceptable risk, efforts have been made to develop systems for limiting the amount of time that the support equipment remains coupled with the vehicle's electrical system. The overall goal of such systems is to prevent the support equipment from reducing the battery voltage to a level that would be insufficient to start the vehicle (e.g., on the order of 11 volts). As a result, the battery is maintained in a condition that will allow the vehicle to be started when this becomes desirable.
Early efforts to accomplish this employed a relatively simple timer function, for disconnecting the equipment from the vehicle's battery after an established period of time. This period of time was selected to be sufficiently short to prevent the battery voltage from dropping below a safe level. After the established period had passed, the equipment was disconnected from the vehicle's battery to prevent the battery from further discharge.
Enhancements were then added to such basic systems to improve their versatility, and to increase the amount of time that the equipment could safely remain connected to the vehicle's battery. For example, voltage level-detecting equipment was added, initially to determine when the battery voltage was approaching an undesirable level, and later to determine when the battery voltage was leaving a range which would be safe for further operations to continue (i.e., over voltage and under voltage detection). Steps were also taken to detect when the vehicle was running, to in such cases allow the equipment to remain connected to the battery (which would at that point be charging responsive to the running vehicle's electrical system) irrespective of the passage of the period of time established for disconnecting the equipment from the vehicle's battery. Other enhancements were similarly developed to improve the versatility of such systems.
Nevertheless, such systems have, to date, exhibited various problems and disadvantages when placed into operation. For example, such systems have tended to provide poor timing accuracy. This can either prematurely disconnect the equipment from the supporting battery, or cause the battery to remain connected to the equipment for too long a period, drawing the battery's voltage down below an acceptable level.
Yet another disadvantage is that previous systems were implemented using analog design methods. As a result, the circuits of such systems were subject to component drift, with temperature and time, and to component tolerances.
Yet another disadvantage is that such systems tended to be unreliable in detecting that the vehicle was running, again leading to system compromises. Previous implementations used analog techniques with very simple state machines. To detect that a vehicle is running, fast signal capture and the detection of running signals over an extended period of time (e.g., 1 to 4 seconds) is required to reduce the system's susceptibility to noise. Analog techniques have a difficult time accommodating this requirement. For example, a previously employed technique for detecting a running vehicle uses a fast pulse average energy detection method. The problem with this technique is that the pulse energy during normal engine operation changes widely over time (with engine RPM), making a suitable detector difficult to implement. Such circuits can also fail to distinguish between a single large energy pulse and plural smaller energy pulses having the same total energy.
Yet another disadvantage of such systems is that when a vehicle is started, the voltage condition of the vehicle's battery can be adversely affected by the significant amounts of current that are drawn by the vehicle's starter motor. Depending upon the general condition of the battery, operation of the starter motor can pull the voltage on the battery down to a level which is too low for proper operation of the equipment which is being supported by the battery. This can, in turn, cause such equipment to shut down to the extent that it becomes necessary to re-start (i.e., re-boot) such equipment. This commonly results in an undesirable loss of volatile memory. For example, data and/or temporary files can be lost, and data transfers then in progress can be discontinued.
Moreover, irrespective of their manner of operation, such systems will at some point operate to disconnect the equipment which is being supplied with power from the vehicle's battery. For systems using a simple timer, this will occur after the set period of time passes. For systems with more enhanced functions, this may be delayed to some extent through the detection of voltages, or by monitoring other system parameters. Ultimately, however, the equipment will at some point be disconnected from the battery which is to supply that equipment with the power needed for its continued operation. It would be beneficial to extend the period of time available before such equipment had to be disconnected from its power source.